1. Field of the Invention
The present invention relates to a plasma display device and a method for driving the same.
2. Description of the Related Art
A plasma display device has been implemented as one type of thin two-dimensional screen display device. A matrix-type surface discharge AC plasma display panel having a memory function is known as one of plasma display devices.
Almost of surface discharge AC plasma display panels employ a three-electrode structure. In this type of plasma display panel, two substrates, i.e., a front glass substrate and a back glass substrate are positioned opposite to each other with a predetermined gap intervening therebetween. On an inner surface (i.e., a surface opposite to the back glass substrate) of the front glass substrate serving as a display plane displaying an image, a plurality of paired row electrodes extending in parallel are formed as paired sustain electrodes. On the back glass substrate, a plurality of column electrodes intersecting with the paired row electrodes are formed to extend as address electrodes, and a fluorescent material is coated overlaying the column electrodes. Between the front substrate and the back substrate airtightly sealed, when viewed from the display plane, cells, i.e., unit light emitting regions each corresponding to a pixel or a light emitting cell are formed in a matrix form, each centered on the intersection of the paired row electrodes and a column electrode. In one cell, a gap between the row electrodes or the transparent electrodes near the intersection functions as a discharge gap. The row electrodes and the column electrodes may be referred to as xe2x80x9cdischarge electrodes.xe2x80x9d
FIG. 1 illustrates the configuration of a driver for driving a plasma display panel 120 which comprises column electrodes D1 to Dm connected to a pixel data pulse generator circuit 212, and paired row electrodes X1, Y1 to Xn, Yn connected to a row electrode driving pulse generator circuit 210.
Referring specifically to FIG. 1, a synchronization separating circuit 201 extracts horizontal and vertical synchronization signals from an input video signal supplied thereto, and supplies a timing pulse generator circuit 202 with the extracted synchronization signals. The timing pulse generator circuit 202 generates an extracted synchronization signal timing pulse based on the extracted horizontal and vertical synchronization signals, and supplies this timing pulse to an A/D converter 203, a memory control circuit 205 and a read timing signal generator circuit 207, respectively. The A/D converter 203 converts the input video signal to digital pixel data corresponding to each pixel in synchronism with the extracted synchronization signal timing pulse, and supplies the digital pixel data to a frame memory 204. The memory control circuit 205 supplies the frame memory 204 with a read signal and a write signal in synchronism with the extracted synchronization signal timing pulse. The frame memory 204 sequentially fetches respective pixel data supplied from the A/D converter 203 in response to the write signal. Pixel data stored in the frame memory 204 is sequentially read therefrom in response to the read signal and supplied to an output processing circuit 206 at the next stage. The read timing signal generator circuit 207 generates a variety of timing signals for controlling a discharge light emission operation, and supplies these timing signals to the row electrode driving pulse generator circuit 210 and to the output processing circuit 206. The output processing circuit 206 supplies the pixel data pulse generator circuit 212 with pixel data supplied from the frame memory 204 in synchronism with a timing signal from the read timing signal generator circuit 207.
The pixel data pulse generator circuit 212 generates a pixel data pulse DP corresponding to each of pixel data supplied from the output processing circuit 206, and applies the pixel data pulse DP to the column electrodes D1-Dm of the plasma display panel 120.
The row electrode driving pulse generator circuit 210 generates first and second predischarge pulses for performing a predischarge between all pairs of row electrodes X1, Y1 to Xn, Yn in the plasma display panel 120, a priming pulse for re-forming charged particles, a scan pulse for writing pixel data, a sustain pulse for sustaining a discharge for emitting light in accordance with pixel data, and an erasure pulse for stopping the discharge sustained for light emission. The row electrode driving pulse generator circuit 210 supplies to the row electrodes X1-Xn and Y1-Yn of the plasma display panel 120 with these pulses at timings corresponding to a various types of timing signals supplied from read timing signal generator circuit 207.
The row electrode driving pulse generator circuit 210 includes an X-driver for generating a sustain pulse for the row electrodes X1 to Xn, and a Y-driver for generating a sustain pulse for the row electrodes Y1 to Yn.
For driving a surface discharge AC plasma display panel having a plurality of pixel cells formed in matrix, it is necessary to select whether or not each pixel cell is to emit light in each sub-frame. In this event, for providing a uniform difference in light emitting condition between pixel cells due to the difference in data for images to be displayed in each sub-frame, and also for stabilizing a discharge when writing data, a rectangular reset pulse is applied between row electrodes of the paired row electrodes to initialize all cells by the action of a reset discharge caused by the application of reset pulse. Next, a rectangular scan pulse is applied to the column electrodes selected in accordance with data to cause selective discharges between the selected column electrodes and associated row electrodes to write data into corresponding pixel cells.
In the initialization of and the data write into pixel cells, there are two possible processes. First, selective writing is performed for selecting pixel cells, from which light is to be emitted, by previously generating a constant amount of wall charges in all pixel cells by the reset discharge and increasing the wall charges in the pixel cells by a so-called selective discharge using a scan pulse applied to selected column electrodes. Second, a selective erasure is performed for selecting pixel cells to be maintained unlit by extinguishing wall charges in the pixel cells by a selective discharge. Subsequently, a sustain pulse is applied to produce a sustaining discharge for maintaining emitted light in selected pixel cells during the selective write or to produce a sustaining discharge for maintaining emitted light in non-selected pixel cells during the selective erasure. Further, after a predetermined time has elapsed, data written in pixel cells is erased by applying erasure pulses to the pixel cells in any data write.
FIG. 2 conceptually illustrates the configuration of an X-driver 210X and a Y-driver 210Y in a row electrode driving pulse generator circuit 210. Referring specifically to FIG. 2, the pulse generator circuit 210 comprises a sustain voltage source Vs; switches SW1-SW5 such as FETs; a charge recovering capacitor CK; coils LK1, LK2; and diodes D1, D2 each for regulating a current to flow in a single direction. In this configuration, a series resonance circuit is formed of the capacitor CK and the coil LK1 or LK2.
A driving method for generating a sustain pulse to row electrodes X1-Xn by the X-driver 210X will now be described with reference also to FIGS. 3A and 3B. FIG. 3A illustrates the charging voltage waveform of a sustain pulse applied to a row electrode, and FIG. 3B illustrates a change in the luminance of emitted light from an associated cell. Assume that a charge has been sufficiently recovered to the capacitor CK from a panel after the switch SW2 has been turned ON and the remaining switches have been turned OFF after application of the preceding sustain pulse. First, the switch SW5 is turned ON and the remaining switches are turned OFF to reduce the potentials at all of the row electrodes X1-Xn to the ground potential. Next, the switch SW1 is turned ON and the remaining switches are turned OFF at timing T1, causing the charge on the capacitor CK to be supplied to the row electrodes X1-Xn through the coil LK1 and the diode D1. Thus, charging is started on all of the row electrodes X1-Xn with the charge on the capacitor CK forming part of the series resonance circuit. Then, as the switch SW4 is turned ON and the remaining switches are turned OFF at timing T2 after a predetermined time during which it is expected that the panel exhibits a maximally charged voltage (ideally, a quarter wavelength of the resonance frequency), the row electrodes X1-Xn are supplementarily supplied with charges such that they hold the sustain pulse which has a voltage raised to the voltage of the sustain voltage source Vs. In this way, the charge of the panel previously recovered on the capacitor CK can be used to previously charge the panel for the next time. As illustrated in FIG. 3A, timing T3 indicates a start timing for turning the switch SW2 ON to recover a charge of the panel to the capacitor CK, and timing T4 indicates a start timing for turning the switch SW5 ON to switch to the ground potential. The duration between the timings T3 and T4 may be given by a predetermined time Txcex1xe2x80x2 similar to Txcex1.
As described above, in the conventional driving method for generating a sustain pulse to the row electrodes X1-Xn through the X-driver 210X, the voltage waveform of the sustain pulse for minimizing the power is generated as a rectangular pulse having abrupt rising and falling edges between timings T1 and T4. More specifically, as illustrated in FIG. 3A, the switch SW1 is turned ON at timing T1 to start rapid charging of the panel with a recovered charge on the capacitor CK, and the switch SW1 is turned OFF and the switch SW4 is turned ON to switch a charged voltage to the constant voltage source Vs, thus continuously charging the panel at timing T2 after a predetermined time Txcex1 during which a peak voltage VCHG available from the series resonance circuit is reached. Thus, as illustrated in FIG. 3B, the luminance of light emitted from a plurality of cells increases substantially simultaneously at timing T2. Likewise, a pixel data pulse, a scan pulse and an erasure pulse are each generated as a rectangular pulse having abrupt rising and falling edges.
In the prior art, on the other hand, an opaque metal material is used for bus electrodes. Thus, when rectangular sustain pulses are applied so that the charging extends from the row electrodes or the transparent electrodes to bus electrodes, visible light generated within each cell of a panel is shielded by the bus electrodes in a greater ratio, thus resulting in a reduced light emitting efficiency. Also, as the applied voltage Vs of the sustain pulse is increased, the panel experiences a reduced light emitting efficiency.
To solve the problem of the reduction in light emitting efficiency, the applied constant voltage Vs generated by an external sustain voltage source for the sustain pulse is set near a minimal discharge sustaining voltage Vsm inherent to cells, as illustrated in FIG. 3A, in order to concentrate the discharge on edges of leading ends of opposing transparent electrodes to reduce the ratio of light shielded by the bus electrodes and accordingly improve the light emitting efficiency. Since power consumption is governed by a potential difference between the peak voltage VCHG and the constant voltage Vs, the power consumption can be reduced by minimizing this potential difference between the two voltages.
In this case, however, if the minimal discharge sustaining voltage Vsm inherent to cells largely varies with respect to the externally applied voltage Vs during a panel manufacturing process, a certain cell will fail to emit light if the externally applied voltage Vs does not reach a minimal discharge sustaining voltage Vsmxe2x80x2 inherent to the cell, as illustrated in FIG. 3A, in spite of the externally applied voltage Vs which is set at a value equal to or higher and near a minimum value of minimal discharge sustaining voltage Vsm of a plurality of cells. As mentioned, the prior art driving method has a problem that stable light emission is hindered by variations in the discharge characteristic of each of cells constituting a panel.
Furthermore, in the prior art, the timing T2 (or T4) for switching a charged voltage VCHG to the constant voltage source is determined by a fixed time Txcex1(or Txcex1xe2x80x2), as illustrated in FIG. 3A. If variations in capacitance of cells in an overall panel cause the resonance frequency of a series resonance circuit to shift, for example, in a direction in which the timing Txcex1 becomes smaller, the charged voltage VCHG is switched to the constant voltage source before it reaches a peak value of the resonance waveform due to the abrupt rising of the sustain pulse, causing an unstable potential difference between the charged voltage VCHG and the externally applied voltage Vs. This potential difference is difficult to minimize, and may also cause a problem of larger power consumption.
It is therefore an object of the present invention to achieve a plasma display device and a method for driving the same being capable that a stable micro-discharge at a lower voltage by optimizing the waveform of a sustain pulse applied to row electrodes and the structure of cells to improve a light emitting efficiency. It is another object of the present invention to stabilize light emitted from cells in spite of variations in the discharge characteristic of respective cells constituting the plasma display panel.
To achieve the above object, the present invention provides a plasma display device for displaying an image comprising:
a plasma display panel including a plurality of row electrodes formed in pairs and extending in parallel with each other in the horizontal direction, a plurality of column electrodes extending in the vertical direction and facing said paired row electrodes with a discharge space intervening therebetween to form unit light emitting regions at respective intersections with said paired row electrodes, and a dielectric layer for covering up said paired row electrodes with respect to said discharge space;
means for applying a scan pulse to every pair of row electrodes and simultaneously applying a pixel data pulse to every column electrode to select light emitting pixels and non-light emitting pixels during an addressing period; and
means for applying a series of sustain pulses alternately to one of the row electrode pair and the other thereof to sustain discharges for said light emitting pixels and said non-light emitting pixels during a discharge sustaining period, wherein each of said sustain pulses has a waveform exhibiting gentle rising or falling at a leading edge thereof, as compared with said scan pulse, whereby limiting each of said sustaining discharges in a region near a discharge gap formed between paired row electrodes within said unit light emitting region.
In a plasma display device in an aspect of the invention, a protruding surface portion is formed on said dielectric layer to protrude relative to the remaining surface portion of said dielectric layer, said protruding portion being positioned on an edge portion of said row electrode on the side opposite to said discharge gap, whereby further limiting each of said sustaining discharges in a region near a discharge gap formed between paired row electrodes within said unit light emitting region.
In a plasma display device in another aspect of the invention, each of said row electrodes is formed with a width equal to or more than 300 xcexcm within said unit light emitting region, whereby further limiting each of said sustaining discharges in a region near a discharge gap formed between paired row electrodes within said unit light emitting region.
In a plasma display device in another aspect of the invention, each of said paired row electrodes includes a main portion extending in the horizontal direction, and a protrusion protruding from said main portion in the vertical direction so as to face a protrusion of the other row electrode forming a pair, with a discharge gap intervening therebetween, in each of said unit light emitting regions, whereby further limiting each of said sustaining discharges in a region near a discharge gap formed between paired row electrodes within said unit light emitting region.
In a plasma display device in another aspect of the invention, said protrusions are formed such that said discharge gap is formed in the horizontal direction.
In a plasma display device in another aspect of the invention, said protrusions are formed such that said discharge gap is formed in the vertical direction.
In a plasma display device in another aspect of the invention, said regions of the respective row electrodes in said paired row electrodes near said discharge gap are formed opposite to each other face to face with said discharge space intervening therebetween, whereby further limiting each of said sustaining discharges in a region near a discharge gap formed between paired row electrodes within said unit light emitting region.
In a plasma display device in another aspect of the invention, said means for applying the sustain pulses comprises:
a DC power source for generating DC voltage having a positive side and negative side terminals;
a first capacitor connected in parallel with said DC power source;
a coil having a fist end connected to the positive side terminal of said DC power source and a second end opposite thereto;
switching means for alternately performing a connection and a disconnection between the second end of said coil and the negative side terminal of said DC power source;
a diode having a cathode connected to the second end of said coil and an anode connected to the negative side terminal of said DC power source; and
a second capacitor connected in parallel with said diode, wherein said coil outputs the sustain pulse at the second end thereof in accordance with an operation of said switching means.
In a plasma display device in another aspect of the invention, a change rate of the voltage value gently increasing of said sustain pulse in said unit light emitting region is 50volts or less per microsecond.
In a plasma display device in another aspect of the invention, said sustain pulse which exhibits gradually rising is selected from a group composed of pulse waveforms having a saw-tooth wave, a triangular wave and a sinusoidal wave.
According to the present invention, a series of sustain pulses are applied the paired row electrodes to sustain discharges for light emission during a discharge sustaining period, wherein each of the sustain pulses has a waveform gradually or gently rising or falling at a leading edge thereof, as compared with the scan pulse, whereby limiting each of the sustaining discharges in a region near a discharge gap formed between paired row electrodes within the unit light emitting region. Therefor the plasma display device provides a more stabilized micro-discharge in all cells of the overall panel in the plasma display device, thereby making it possible to simultaneously improve a light emitting efficiency and ensure a display margin.